1. Field of the Invention
The invention relates to highway safety methods and structures and refers more specifically to determining the condition of a highway surface or the like and providing an indication thereof, particular structure for providing a signal proportional to the speed of an electric motor from the motor itself, and a method of and structure for motor speed control with the particular structure.
2. Prior Art
There is considerable emphasis today on highway safety. As a result, automobile manufacturers and highway engineers are attempting to improve the safety of both automobiles and highways. There are, however, many parameters of highway safety which are beyond the control of automotive and highway engineers. One of the significant parameters influencing highway safety is weather conditions. Weather conditions may produce particularly dangerous highways due to the degree of slipperiness of the road surface.
In the past, attempts have been made to determine the condition of a road surface and to warn approaching motorists when the road surface condition is dangerous. Such attempts have often taken the form of instruments for measuring the dew point and temperature to determine the existence of, for example, water or ice on a highway. However, such devices have not been the ultimate answer since highway surfaces may be slippery without water or ice thereon. For example, small granules of sand distributed on the surface of a highway will seriously reduce the coefficient of friction of the surface so that vehicle tires may slide on the road surface. Therefore, it is desirable to more exactly measure the coefficient of friction or slipperiness of a road surface rather than specific conditions thereof, such as the presence of water or ice thereon.
In addition, wherein motor speed control devices have been provided in the past, they have generally included separate equipment, such as tachometers to provide a feedback signal proportional to motor speed. Such additional equipment is expensive and not essential in motor speed control apparatus.
Also, prior speed controls for electric motors have not usually been fail safe. That is, they have not included structure for preventing operation of the motor if the motor speed control circuit malfunctions. A fail safe motor control circuit is particularly desirable in conjunction with electrically driven automobiles and the like.